This invention relates to improvements in vapor jacketed cooking vessels which integrally contain fired vapor generators, thus making them independent of outside vapor supply.
Vapor jacketed cooling vessels of the above-described type are used for the concentration, cooking and heating of a wide variety of liquids, slurries, emulsions and other like products where the vessel wall temperature must be controlled to prevent damage to the contained product. They are available in many standard sizes and built to any practical size. The construction basically is to enclose the vessel in an appropriate jacket which will thus surround the major portion of the vessel with hot vapor, which vapor condenses on the outside of the vessel and transfers heat thereto. An appropriate quantity of working fluid is kept in the jacket, and the vapor is generated in the evaporator portion of the jacket, which is usually the bottom thereof. The most common working fluid is water, although numerous other fluids such as alcohol, glycol, Freons, Dowtherms and the like are well known and have been widely used. The vapor space between the vessel and the jacket is evacuated of all air and other permanent gases (which would seriously interfere with the heat transfer) and the system then operates at an absolute pressure which is established by the temperature of the working fluid, this temperature being the balance between the rates of heat input to the liquid and the rate of vapor condensation on the exterior of the vessel. With water as the working fluid, when at room temperature, this pressure can fall to well under one inch mercury absolute. The condensate forming on the vessel exterior drains down and drips back into the boiling pool at the bottom of the jacket.
The usual method of firing the jacket is to place a burner under it, and to enclose the space around the jacket with an insulated shell so that the hot gases from the burner wash over the jacket bottom and walls and thereby heat and boil the contained working fluid. Such practice leads to a bulky, expensive construction, and even with the addition of fins or the like to the jacket exterior, the heat absorption is slow and the overall efficiency not high. Although the overall result of this orthodox construction has been broadly used, the industry has spent considerable time and effort in trying to develop an improved means for heating these vessels.
One attempt at improvement has been to provide a tubular evaporator which protrudes from the jacket, this evaporator being lined with a wick so that the assembly performs as a heat pipe. Such wicked heat pipes, however, have relatively low heat moving capacity for any given diameter, and for many applications in which these jacketed vessels are utilized, their use results in a construction so large as to be uneconomical and unacceptable. A tubular evaporator of this type, and one which is typical of this configuration, is shown in U.S. Pat. No. 3,791,372, wherein the very large cross-section of the evaporator tube is clearly apparent.